This project attempts to employ matrix theories in constructing a probabilistic model for projecting population by region. The analysis can be viewed as an extension of the previous contribution made by Leslie (1945), Keyfitz (1964), Tarver (1965), Roger (1968), and many others. In this project, population projection is treated as an open system and the inter-regional flows of population are considered. By drawing on the merits and eliminating the defects of various previous models, this project expects to achieve a more realistic projection of regional population distribution.